The Battle of Nagyszeben was a World War I military engagement fought between the forces of the Central Powers (Germany and Austria-Hungary) on one side and the forces of Romania on the other side. It was the decisive engagement during the Battle of Transylvania, and also the largest, involving four armies out of the five fighting in the region: two Romanian, one German, and one Austro-Hungarian.
German General Erich von Falkenhayn planned to surround and annihilate the entire I Corps of General Ioan Culcer's Romanian 1st Army. Although this failed - the bulk of the Romanian force including almost its entire artillery managing to escape - the battle was still decisive in that it compelled the Romanian abandonment of Transylvania. Midway into the battle, the Romanian 2nd Army tried to relieve the besieged I Corps, attacking both the flank of the German 9th Army and the western flank of the Austro-Hungarian 1st Army. Thus, in the second half of the battle, two more armies joined the fray.
Background
At the onset of the Romanian Campaign, starting on 27 August 1916 with the Battle of Transylvania, the Romanian 1st Army, under the command of General Ioan Culcer, consisted of six divisions, of which four comprised the I Corps, under the command of General Ioan Popovici. In the middle of September, General Culcer moved the I Corps headquarters to Nagytalmács (Tălmaciu/Talmesch). General Popovici arrived in Nagytalmács along with his staff on 16 September. Popovici had two divisions under his command at Nagyszeben (Sibiu/Hermannstadt): the 13th and the 23rd. While concentrating their forces northwest of Nagyszeben in preparation for the impending battle for that city, the Germans kept the Romanians under artillery fire in order to keep them from sending out patrols that could have discovered the German build-up. Romanian frustration with having to endure this bombardment boiled over, and on 22 September General Popovici ordered his 13th Division to take the heights at Veresmart (Roșia/Rothberg), east of Nagyszeben. Although this action was against Culcer's orders, it was still Culcer himself who decided to appoint Popovici as commander of the two Romanian divisions headquartered at Nagytalmács. Although Popovici's attack failed in its immediate aim, it succeeded in worsening the strategic situation of the Central Powers, driving a wedge between the two divisions of a German-led Cavalry Corps. If exploited, this wedge could ruin the German plans to secure Nagyszeben (Sibiu/Hermannstadt). On the following day (23 September), the German Alpine Corps began their march through the mountains to the Red Tower pass, behind Romanian lines.Michael B. Barrett, Indiana University Press, Oct 23, 2013, Prelude to Blitzkrieg: The 1916 Austro-German Campaign in Romania, pp. 103-107 During the march of the German Alpine Corps, the left of the Central Powers forces - the German column which was to encircle the Romanians from the east - succeeded in forcing the crossing of the Olt River at Kolun (Colun/Kellen), east of Porumbák. Thus, an effective barrier was created between the 1st and the 2nd Romanian armies. In its advance across the mountain ridge separating the valleys of the Hortobágy (Hârtibaciu/Haarbach) and Olt Rivers, this German column was faced with determined resistance. Still, its numerical superiority enabled it to prevail.The Times, 1917, The Times History and Encyclopaedia of the War, Volume 11, p. 228John Buchan, T. Nelson, 1922, A History of the Great War: From the battle of Verdun to the third battle of Ypres, p. 233 By the evening of 25 September, Kolun was in German hands.Edmund Glaise-Horstenau, Österreich-Ungarns letzter Krieg 1914 – 1918. Vol. 5: Das Kriegsjahr 1916; 2; Beil, Verl. der Militärwiss. Mitteilungen, Wien, 1932
Falkenhayn's plan On 19 September, Erich von Falkenhayn assumed command of the German 9th Army. This army subsequently started assembling the bulk of its forces near Nagyszeben. Von Falkenhayn divided his forces into three groups: the XXXIX Reserve Corps, the Alpine Corps and Cavalry Corps Schmettow. His plan was bold: the annihilation of the Romanian units around Nagyszeben. Konrad Krafft von Dellmensingen's Alpine Corps Division was to act as an anvil, seizing the Red Tower Pass in order to block a Romanian retreat. Hermann von Staabs's Corps, assembling northwest of Nagyszeben, was to act as a hammer, driving southeast towards the mouth of the Red Tower Pass at Nagytalmács (Tălmaciu/Talmesch). With the Alpine Corps blocking the Romanian line of retreat, the XXXIX Corps would smash the Romanians against the mountains. Von Schmettow's cavalry had to maintain contact with the Austro-Hungarian 1st Army, make sure that none of the Romanians escaped east, and block any reinforcements coming from the Romanian 2nd Army, threatening the 9th Army's flank.Michael B. Barrett, Indiana University Press, Oct 23, 2013, Prelude to Blitzkrieg: The 1916 Austro-German Campaign in Romania, pp. 100 and 102-103 Popovici relied on the mountains to protect his flanks. However, reconnaissance by the German Alpine Corps revealed that it was possible to bypass his western flank, on foot, through the mountains, then reach and cut off the Romanian line of retreat. This made Popovici's corps the most tempting target, and von Falkenhayn stressed as much: all else was secondary to striking a decisive blow at Nagyszeben.Prit Buttar, Bloomsbury Publishing, Sep 22, 2016, Russia's Last Gasp: The Eastern Front 1916–17, pp. 341 and 344
Units involved (forces and deployments) On the Romanian side, General Popovici had two divisions at Nagyszeben: the 23rd Division to the south and west of the highway running from Nagyszeben to the Red Tower Pass and the 13th Division to the east of this highway. The 23rd was commanded by General Matei Castriș and the 13th by General Ioan Oprescu. The two divisions formed the I Corps, headquartered at Nagytalmács since 16 September. The Romanian divisions occupied a line of 25 miles, a large distance even by Eastern Front standards. General Popovici kept his units in the forward trenches, meaning that - given the length of the front - there were no reserves and no depth. General Culcer - Popovici's superior as overall commander of the Romanian 1st Army - was aware of these issues, but his attempts to get Popovici to shorten his lines and form a reserve were unsuccessful.Michael B. Barrett, Indiana University Press, Oct 23, 2013, Prelude to Blitzkrieg: The 1916 Austro-German Campaign in Romania, pp. 103-104 and 106-107 The Romanian front extended east and west, with Sellenberk (Șelimbăr/Schellenberg) for its center. To the east, the extreme right wing of the Romanian lines reached Porumbák (Porumbacu/Bornbach), in the valley of the Olt River. To the west, the Romanian front extended to the Szecsel (Săcel/Schwarzwasser) - Orlát (Orlat/Winsberg) - Popláka (Poplaca/Gunzendorf) line. A gap of 15 miles intervened between the extreme right of this front (Porumbák) and the vanguard of the Romanian 2nd Army, west of Fogaras (Făgăraș/Fogarasch). The left wing of this Romanian group had no connection either to the west or to the south. The two wings extended like the branches of a tree, their trunk being the road and railway going through the Red Tower Pass. Over 10 miles of tall mountains separated this Romanian front from the Romanian border.The Times, 1917, The Times History and Encyclopaedia of the War, Volume 11, p. 226 The Romanians were supplied by only one railway line, while von Falkenhayn had three supply lines.Lieutenant-Colonel E. M. Benitez, Command and General Staff School, 1939, Quarterly Review of Military Literature, Volume 19, Issue 73, p. 9 Prisoners had revealed to Culcer on the 24th that two German regiments had entered the mountains. Culcer passed this information on to Popovici, adding that it was confirmed by two other reports. In response to these reports, Popovici sent two battalions into the mountains: one battalion and some guns for the protection of the Red Tower Pass and another battalion was dispatched to protect the regions west of the pass.Michael B. Barrett, Indiana University Press, Oct 23, 2013, Prelude to Blitzkrieg: The 1916 Austro-German Campaign in Romania, pp. 106-107Curtis Brown, Stackpole Books, Feb 1, 1991, Roots of Strategy: Book 3, p. 459
The German XXXIX Corps, under General Hermann von Staabs, comprised the 187th Prussian Division (General Edwin Sunkel), the 51st Honvéd Division (General Béla Tanárky) and the 76th Prussian Reserve Division (General Hugo Elster von Elstermann). When the battle began at dawn on 26 September, Von Staabs had his divisions arrayed with the 76th Reserve Division on the east flank, the 51st Honvéd in the center and the 187th Division to the west.Michael B. Barrett, Indiana University Press, Oct 23, 2013, Prelude to Blitzkrieg: The 1916 Austro-German Campaign in Romania, pp. 102, 107-108, 390, 397-398 The cavalry group under General Eberhard Graf von Schmettow comprised the 1st Austro-Hungarian and 3rd German Cavalry Divisions. Both units were under the direct command of von Schmettow, initially the commander of only the 3rd Division.Michael B. Barrett, Indiana University Press, Oct 23, 2013, Prelude to Blitzkrieg: The 1916 Austro-German Campaign in Romania, p. 99 General Krafft's Alpine Corps comprised the Jäger Brigade (Brigadier General Ludwig Ritter von Tutschek) and the Bavarian Guard Regiment (Colonel Franz Ritter von Epp).Michael B. Barrett, Indiana University Press, Oct 23, 2013, Prelude to Blitzkrieg: The 1916 Austro-German Campaign in Romania, p. 104